424 Mr. Gr. N. Antonoff on the 



and in some cases the activity does not decay exponentially 

 if measured without absorbing screens. However, the radia- 

 tion passing through O'Ol cm. of aluminium decays normally 

 with the same period as the pure barium preparations. 

 Therefore if the activity of the preparation is measured 

 through 0*01 cm. of aluminium, and the value obtained 

 multiplied by 2*15, the total activity at any time due to UrX 

 alone can be calculated. The UrX activity is then sub- 

 tracted from the total activity to obtain the activity of the 

 product mixed with it. 



The Product. — Its Decay and Absorption. 

 The ferric preparations were examined by the method 

 already described, and several curves were obtained showing 

 that a soft ray product which decays in a few days is always 

 present in small quantity. Several attempts were made to 

 separate a large quantity of this product from uranium, but 

 in all cases its activity is small compared with that of the 

 UrX with which it is separated. Owing to the very similar 

 chemical properties of UrX and the new product, it was 

 not found possible to isolate the latter, for it was always 

 accompanied with UrX*. When UrX and the product are 

 separated from uranium in equilibrium by the ferric method, 

 a preparation is obtained containing so much UrX that it is 

 sometimes difficult to measure its activity with the electro- 

 scope. Further separations bring down less and less of UrX 

 and the product. The separation is then repeated after 

 allowing it to stand for a few days. The new product is 

 then separated with comparatively little UrX. To determine 

 the absorption of the radiation it is necessary to prepare very 

 thin films. For this purpose the method of separation was 

 sometimes modified. The uranium was dissolved in a half 

 normal solution of ammonium carbonate, a trace of ferric 

 salt added, and the solution boiled and filtered. The iron 

 precipitate was washed with ammonium carbonate solution 

 to remove the traces of uranium, and the filter-paper was 

 then burnt ; the ashes in a very thin layer were placed on a 

 tray. In this way, although it was necessary to work with 

 large volumes, it was easy to make the separation with only 

 minute traces of iron. These preparations were examined 

 by the electroscope already described. The decay curves 

 are given in fig. 3. 



* Information on the chemical properties of UrX may be found in 

 the paper by Lloyd, J. of Phys. Chem. xxiv. p. 509 (1910). See als 

 Keetman, Jahr. d. Bad. vi. p. 265 (1909). 



